import http from 'node:http'
import { execFile } from 'node:child_process'
import { createHmac, timingSafeEqual } from 'node:crypto'
import { fileURLToPath } from 'node:url'
import { dirname, join } from 'node:path'
import { config } from 'dotenv'

const __dirname = dirname(fileURLToPath(import.meta.url))
// Shares backend/.env with the audit endpoint rather than keeping a second
// secrets file - one chmod 600 file to manage, not two.
config({ path: join(__dirname, '..', '.env') })

const PORT = Number(process.env.WEBHOOK_PORT ?? 3002)
const SECRET = process.env.WEBHOOK_SECRET
const BRANCH = process.env.WEBHOOK_BRANCH ?? 'refs/heads/master'

if (!SECRET) {
  console.error('WEBHOOK_SECRET is not configured. Refusing to start.')
  process.exit(1)
}

// Only one deploy runs at a time. Two pushes seconds apart would otherwise
// race two concurrent `git reset --hard` + npm install in the same checkout.
let deploying = false

/**
 * Gitea/Forgejo send `X-Gitea-Signature: <hex hmac-sha256 of body>`.
 * GitHub-compatible integrations send `X-Hub-Signature-256: sha256=<hex>`.
 * Accept either so this works regardless of which the instance uses.
 */
function verifySignature(rawBody, header) {
  if (!header) return false
  const provided = header.startsWith('sha256=') ? header.slice(7) : header
  const expected = createHmac('sha256', SECRET).update(rawBody).digest('hex')

  const a = Buffer.from(provided)
  const b = Buffer.from(expected)
  // Length check first: timingSafeEqual throws on mismatched lengths rather
  // than returning false.
  return a.length === b.length && timingSafeEqual(a, b)
}

function runDeploy() {
  if (deploying) {
    console.log('Deploy already in progress, ignoring this push.')
    return
  }
  deploying = true
  console.log('Deploy started.')

  // No shell, no string interpolation - argv is a fixed one-element array.
  execFile(
    'bash',
    ['deploy.sh'],
    { cwd: __dirname, timeout: 5 * 60 * 1000 },
    (error, stdout, stderr) => {
      deploying = false
      if (error) {
        console.error('Deploy failed:', error.message)
        if (stderr) console.error(stderr.trim())
        return
      }
      console.log(stdout.trim() || 'Deploy finished.')
    }
  )
}

const server = http.createServer((req, res) => {
  if (req.method !== 'POST' || req.url !== '/deploy-webhook') {
    res.writeHead(404).end()
    return
  }

  const chunks = []
  let size = 0

  req.on('data', (chunk) => {
    size += chunk.length
    // A webhook payload is a few KB. Anything past 1 MB is not Gitea.
    if (size > 1_000_000) {
      req.destroy()
      return
    }
    chunks.push(chunk)
  })

  req.on('end', () => {
    const rawBody = Buffer.concat(chunks)
    const signatureHeader = req.headers['x-gitea-signature'] ?? req.headers['x-hub-signature-256']
    const signature = Array.isArray(signatureHeader) ? signatureHeader[0] : signatureHeader

    if (!verifySignature(rawBody, signature)) {
      console.warn('Webhook signature mismatch - ignoring request.')
      res.writeHead(401).end()
      return
    }

    let payload
    try {
      payload = JSON.parse(rawBody.toString('utf8'))
    } catch {
      res.writeHead(400).end('Invalid JSON.')
      return
    }

    if (payload.ref !== BRANCH) {
      res.writeHead(200).end(`Ignored (push to ${payload.ref}, watching ${BRANCH}).`)
      return
    }

    // Respond before deploying: Gitea has its own webhook timeout, and the
    // deploy (npm install + restart) can take longer than that.
    res.writeHead(202).end('Deploy queued.')
    runDeploy()
  })
})

server.listen(PORT, '127.0.0.1', () => {
  console.log(`Deploy webhook listening on 127.0.0.1:${PORT}`)
})